Some of the silver halides used for heat-developable light-sensitive materials contain silver iodide crystals in the grain thereof and, therefore, they can be used without using organic silver salts, such as silver chloroiodide, silver iodobromide or silver chloroiodobromide. In such silver halides, the X-ray pattern of silver iodide crystals appears. However, it is advantageous to use silver halides together with organic silver salts, because all of the silver halides known in this art can be used and a higher maximum density can be obtained.
Typical examples of such organic silver salts include silver salts of aliphatic carboxylic acids and silver salts of aromatic carboxylic acids.
Further, there are silver salts of aliphatic carboxylic acids having a thioether group as described in U.S. Pat. No. 3,330,663.
However, these silver salts of carboxylic acids are disadvantageous in that they release acids after reacting with a reducing agent to reduce the pH in the film and thus subsequent development is restrained.
Organic silver salts other than carboxylic acids include silver salts of compounds having a mercapto group or a thione group and derivatives thereof.
In addition, there are silver salts of compounds having an imino group such as silver salts of benzotriazole or derivatives thereof, etc., as described in Japanese Patent Publication Nos. 30270/69 and 18416/70.
However, these silver salts are disadvantageous in that they release a compound which restrains development or, in some cases, causes fog after reacting with a reducing agent. In addition, they sometimes inhibit the functions of spectral sensitizing dyes, and high sensitivity cannot be obtained.